Densimeter

ABSTRACT

A densimeter is provided having a pump which impels a liquid at a constant volume through a fixed orifice. A pressure transducer measures the pressure drop of liquid across the orifice and sends a signal to a microprocessor. A microprocessor determines the density of the liquid which is equal to the pressure drop divided by a constant times the square of a volumetric flow impelled by the pump.

TECHNICAL FIELD

The present invention relates to fuel metering systems, and moreparticularly, to a fuel metering system which incorporates a meter thatmeasures fuel density.

BACKGROUND ART

In jet engine fuel metering systems, it is desirable to control the massflow of fuel to the engine. Most meters which measure mass flow arecomplicated and heavier than available volumetric flow meters.Volumetric flow meters are generally lighter, simpler and more reliablethan mass flow meters. However, a fuel metering system utilizing avolumetric flow meter requires that the fuel density be known so that atrue mass flow may be calculated.

DISCLOSURE OF THE INVENTION

It is, accordingly, an object of this invention to determine fueldensity in a simple, reliable manner.

It is a further object of the invention to provide a simple, reliablefuel metering system.

According to the invention, a densimeter is provided which impels aconstant volumetric fuel flow through a fixed orifice of known area. Thedensimeter includes a transducer which measures a pressure drop acrossthe orifice so that fuel density may be calculated.

Further according to the invention, a fuel metering system is providedwhich includes the densimeter, a volumetric flow meter, a metering valveand a microprocessor.

The foregoing, and other features and advantages of the presentinvention, will become more apparent in light of the following detaileddescription and accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a schematic view of the fuel metering system of theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the drawing, an embodiment of a fuel metering system 10 isshown. Generally, fuel is impelled through a conduit 12. The conduitpasses through a volumetric flow meter 14 and a metering valve 16 whichmeters the flow to a gas turbine engine 18. The metering valve metersfuel to the engine as a function of the volumetric fuel flow and thedensity of the flow. The density of the fuel is determined by adensimeter 20.

A line 22 branches off the conduit to provide fuel to the densimeter 20and to return the fuel to the conduit after the density of the fuel iscalculated. The densimeter consists of a pump 24 (as is well known inthe art) which impels the fuel at a constant volumetric flow through afilter 26, a fixed orifice 28 of known area, and a second filter 30downstream of the orifice. A transducer 32 (as is well known in the art)compares the pressure upstream and downstream of the orifice via lines34, 36. The transducer transmits a signal to a microprocessor 38 (as iswell known in the art) where the density of the fuel is calculatedaccording to the following equation:

    ρ=ΔP/(KQ.sup.2)

where

ρ=density in pounds per cubic inch

ΔP=pressure drop across the orifice

K=constant

Q=volumetric flow passing from the pump.

The volumetric flow meter determines the flow of the fuel and inputssuch information to the microprocessor 38.

The microprocessor may then calculate mass flow as a function of theinput from the volumetric flow meter and the densimeter according to theequation:

    W.sub.F =ρV

where

W_(F) =mass flow in pounds per second

ρ=density in pounds per cubic inch

V=volumetric flow in cubic inches per second

The microprocessor may then use the mass flow data to accuratelyposition the metering valve to meter the mass flow of fuel to the engineas required.

While the present invention has been illustrated and described withrespect to a particularly preferred embodiment thereof, it will beappreciated by those skilled in the art, that various modifications tothis system may be made without departing from the present invention.Specifically, the densimeter may have other applications besides fuelmetering. For instance, the densimeter may be particularly useful inscientific experimentation, in the packaging industry, or where ever thedensity of a fluid must be known. Thus it will be understood that thefollowing claims cover the embodiment described herein and all suchequivalent thereof as fall within the true spirit and scope of thisinvention.

Having best described the invention, what is claimed is:
 1. Apparatusfor metering fuel to gas turbine engine:a metering valve; a meter formeasuring the volumetric flow of said fuel and for sending a firstsignal corresponding to said volumetric flow; means for impelling aportion of said fuel at a constant volumetric flow along a flow path; anorifice having a fixed area disposed within said flow path, said portionof said fuel flowing through said orifice; means for determining apressure drop of said fuel across said orifice and for sending a secondsignal corresponding to said determined pressure drop; and means forreceiving said first and second signals to determine mass flow as afunction of volumetric flow and said determined pressure drop toaccurately position said metering valve as required.
 2. Apparatus formetering fuel to a gas turbine engine:a metering valve; a meter formeasuring a volumetric flow of said fuel and for sending a first signalcorresponding to said volumetric flow; means for impelling a portion ofsaid fuel at a constant volumetric flow along a flow path; an orificehaving a fixed area disposed within said flow path, said portion of saidfuel flowing through said orifice; means for determining a pressure dropof said fuel across said orifice and for sending a second signalcorresponding to said determined pressure drop, said pressure dropchanging as a function of a density of said fuel; and means forreceiving said first and second signal to determine mass flow as afunction of said volumetric flow and said pressure drop to accuratelyposition said metering valve as required.